Deposition of Compositionally Graded Mullite/Alumina Coatings from Mixtures of SiCl₄, AlCl₃, CO₂ and H₂

Abstract

Using CVD, compositionally graded coatings of mullite (3 Al 2 O 3´2 SiO 2 ) and alumina (Al 2 O 3 ) were deposited on Si-coated substrates from mixtures of silicon tetrachloride, aluminum trichloride, carbon dioxide, and hydrogen. The coatings were compositionally graded, with the Al/Si ratio increasing towards the outer layer of the coatings. The preparation of the coatings was carried out in a vertical, hot-wall CVD reactor. The results of previous experimental studies on the deposition of aluminosilicate species have been used to identify operating conditions where deposition of coatings with alumina content equal to, or greater than, that corresponding to stoichiometric mullite was possible. The scheme for the preparation of the graded mullite/alumina coatings was based on utilizing the positive effect of decreasing the residence time of the reactive mixture in the reactor, and of increasing the Al/Si ratio in the feed on the incorporation of Al 2 O 3 in the deposit.

Influencing Factors towards a Scalable Synthesis of Aligned Carbon Nanotubes by Chemical Vapour Deposition

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Synthesis of Al2O3–SiO2 Films by Ar/O2 Plasma-Enhanced CVD from Alkoxide Precursors

“…[6][7][8][9][10][11][12][13][14] The disadvantage of using these chloride precursors is that chlorine is hazardous and may cause exhaust pollution. Alkoxide solutions are also important precursors as they have the advantages of low cost, no emission of halogen pollutants, and ease of handling.…”